com.mongodb.DBRef Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2014 MongoDB, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
// DBRef.java
package com.mongodb;
import org.bson.BSONObject;
/**
* Extends DBRefBase to understand a BSONObject representation of a reference.
*
* While instances of this class are {@code Serializable}, deserialized instances can not be fetched,
* as the {@code db} property is transient.
*
* @dochub dbrefs
*/
public class DBRef extends DBRefBase {
private static final long serialVersionUID = -849581217713362618L;
/**
* Creates a DBRef
* @param db the database
* @param o a BSON object representing the reference
*/
public DBRef(DB db , BSONObject o ){
super( db , o.get( "$ref" ).toString() , o.get( "$id" ) );
}
/**
* Creates a DBRef
* @param db the database
* @param ns the namespace where the object is stored
* @param id the object id
*/
public DBRef(DB db , String ns , Object id) {
super(db, ns, id);
}
// Required for serialization framework
private DBRef() {
super();
}
/**
* fetches a referenced object from the database
* @param db the database
* @param ref the reference
* @return the referenced document
* @throws MongoException
*/
public static DBObject fetch(DB db, DBObject ref) {
String ns;
Object id;
if ((ns = (String)ref.get("$ref")) != null && (id = ref.get("$id")) != null) {
return db.getCollection(ns).findOne(new BasicDBObject("_id", id));
}
return null;
}
}